Science 9 - Behind the Bohr Diagram

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BEHIND THE BOHR DIAGRAM
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Line Spectra

• Phenomena which allowed Neil Bohr to develop his
  Planetary Model of the bohr diagram

• Key Idea
• When matter is heated, it produces light
• Think a lightbulb
• Lightbulb is heated to 2200?C

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A lightbulb?
FILAMENT
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Light Spectra

• Passing sunlight through a prism breaks the light
  down into a spectrum of colours

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Light Spectra

• When exposed to light/electricity pure elements
  give out a light

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Light Spectra

• Many elements will emit a specific colour, most
  generally emit red light

ARGON GAS Emits high energy blue light
NEON GAS Emits low energy red light
KRYPTON GAS Emits mid energy yellow light
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Light Spectra

• If you pass this light through a prism, every
  single element has its UNIQUE SPECTRUM

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Light Spectra
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SODIUM
MERCURY
LITHIUM
HYDROGEN
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Light Spectra
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Light Spectra
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So Whats Happening?

• Bohr had two key questions
• Why does matter emit light when heated?
• Why is the light spectra unique for each element?

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Planetary Model of the Atom

• Orbits
• Electrons are found in areas around the nucleus
  called orbits
• Each orbit is an energy level
• Orbits further from the nucleus INCREASE IN
  ENERGY

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• Atoms can exist in two states the ground state or
  an excited state

GROUND STATE
EXCITED STATE
ENERGY

• Normal low energy state of atoms
• Electrons are in lower energy orbits

• Electrons jump to higher energy orbits
• Atoms can not remain in this excited state

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• But why is light released?

GROUND STATE
EXCITED ATOM

• Electrons can not remain at higher energy orbits
• They fall back to their ground orbits but this
  releases light !

• Atom currently in excited state
• Electrons can not remain in excited state

• Normal state of atoms, electrons at lower energy
  level

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A lightbulb?
FILAMENT
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But why do atoms have a unique light spectra?
SODIUM
SODIUM
LITHIUM
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But why do atoms have a unique light spectra?

• The collection of narrow bands of light energy is
  referred to as an emission line spectrum, and the
  individual bands of light are called spectral
  lines.

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Planetary Model of the Atom

• Electrons in an atom move in circular paths
  called orbits found outside of the nucleus of the
  atom

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Planetary Model of the Atom

1. Each electron in an orbit, carries a specific
   amount of energy
2. The farther away the electron is from the
   nucleus, the more energy it has

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Planetary Model of the Atom

1. The order of filling electrons in the first three
   orbits is 2,8,8
2. Electrons are more stable at lower energy levels
   closer to the nucleus